fix: erpnext image build

improve travis.py
python packages not installed in editable mode
use venv module instead of virtualenv

build/frappe-worker/Dockerfile

@@ -32,11 +32,11 @@ RUN install_packages \
 RUN mkdir -p apps logs commands /home/frappe/backups
 
 # Setup python environment
-RUN virtualenv env \
+RUN python -m venv env \
     && . env/bin/activate \
     && cd apps \
     && git clone --depth 1 -o upstream https://github.com/frappe/frappe --branch ${GIT_BRANCH} \
-    && pip3 install --no-cache-dir -e /home/frappe/frappe-bench/apps/frappe
+    && pip3 install --no-cache-dir /home/frappe/frappe-bench/apps/frappe
 
 # Copy scripts and templates
 COPY build/common/commands/* /home/frappe/frappe-bench/commands/